National Motorists Association Blog

High Heels and 4WD

It’s a good idea to skip the high heels if you’re going out for a hike.

Similarly, a two-wheel-drive truck is just about the worst possible choice for attempting to make your way up a steep gravel driveway in summer.

Forget winter.

I rediscovered this truth the other day after not making it up my friend Tim’s steep gravel driveway in my 2WD pick-up. Combine loose gravel (which behaves a lot like snow) a steep incline and a vehicle (my truck) with most of the weight up front — but all the power going to the (light) rear end.

Slip-sliding away…

This same steep gravel driveway did not even faze the low-slung 2016 Acura ILX sport sedan I made the attempt with the next day. Despite the Acura having short-sidewall performance (not off-road) tires and having just a fraction of the ground clearance the truck has.

But the Acura is front-wheel-drive.

It pulls rather than pushes itself.

This is a great advantage. Think of a cat clawing its way up a tree.

And a FWD car’s engine sits on top of the drive wheels, weighting them.

Which is why it’s got more traction than a light-in-the-ass 2WD truck.

This weighting of the drive wheels, incidentally, is also why the old VW Beetle — air cooled model — was such an outstanding snow car. Though rear-wheel-drive, the Beetle’s engine was also rear-mounted. The weight of the engine pushed the tires through the snow, where they usually found at least some purchase. Instead of spinning, you kept moving.

But a front-mounted engine in a rear-drive vehicle = stuck, Chuck. Make that a double if the rear-drive vehicle is a truck — with an empty (and so, light) bed.

This, by the way is why bags of sand or other heavy things are popular carry-alongs in 2WD trucks.

They help… some.

Of course, four-wheel-drive (4WD) would help more — and with the extra ground clearance, you now have what you need for both gravel and deep, unplowed snow.

You have push and pull working together.

And — usually, in a truck-type system — you’ve also got more weight over the front wheels (transfer case) as well as a more even weight spread, front to rear.

Most truck-type systems also have 4WD Low range gearing — which really helps. Mechanical leverage is multiplied; the truck (or SUV, if it has truck-type 4WD) will hunker down — and dig in. With the right tires, such a vehicle can go almost anywhere — including my friend Tim’s god-awful driveway.

Did I mention having to back down? And that his driveway is about a quarter-mile long — and really narrow?

But keep in mind that when you’re not trying to bully your way up a steep gravel driveway (or through deep snow) 4WD should, as a rule, be disengaged — else you risk wear and tear on the parts. Some 4WD systems must be disengaged on dry, smooth roads for exactly this reason. But this leaves you in back in 2WD (rear-wheel-drive) mode — with all the traction disadvantages that attend.

Truck-type 4WD is great on gravel, fabulous in snow. But on dry, paved roads what you probably want is FWD.

Better yet, AWD.

Because it provides a handling as well as a traction advantage.

Some of the newest AWD systems can selectively power (or de-power) individual wheels independently of the others, maximizing lateral grip and stability. For example, the tendency of the car to slide toward the outside of the curve can be counteracted by automatic transfer of engine power one side of the car to the other. Acura’s SH-AWD all-wheel-drive system (not offered with the ILX, incidentally) does exactly this.

Which is why the “SH.”

It stands for Super Handling All Wheel Drive.

Several other manufacturers offer similar systems, including Subaru and Audi.

And most of the latest AWD systems can also split the power, front to rear, from 0 to nearly 100 percent (either way).

They can effectively go from FWD to RWD — to something in between — as conditions indicate.

Truck-type 4WD, in contrast, can only send the power in a fixed proportion (typically, 50 percent to the rear and 50 percent to the front when the 4WD is engaged). And when not engaged, 100 percent of the power goes to the rear wheels.

Slip-sliding away….

The other significant thing to know is that the truck-type 4WD system usually cannot route power to individual wheels, independently of the others. So there’s no handling assist to be had.

Truck-type 4WD is all about traction.

In a (relatively) straight line.

It’s meant for uphills — and downhills.

But not for the curves.

So, to sum up:

If you don’t want to get stuck, skip the 2WD truck. But think carefully before buying the 4WD truck. And give some thought to FWD — or better yet, AWD.

The opinions expressed in posts to the NMA Blog belong to the author and do not necessarily represent those of the National Motorists Association or the NMA Foundation. THe content of the NMA Blog is for informational purposes only and is not intended as legal advice. No representations are made regarding the accuracy of NMA Blog posts or of links found within those posts.

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One Response to “High Heels and 4WD”

This exact problem is what prompted me to buy a third generation Dodge Durango with the 5.7L for my wife. It is normally RWD, but will automatically shunt power to the front wheels as needed. Additionally, it has a 4WD low range that can be manually selected. So, she gets RWD most of the time, power to the front wheels when the rear slips, and if she finds herself stuck she can use 4-low for the best get out of the ditch card short of calling for a tow. It also remedies one of my complaints about AWD vehicles that are primarily FWD: if your front wheels slip and power is applied to rear, that’s great, but your steering is dimished without grip up front. Now, I know that in such situations, the front wheels should find grip quickly or, worst case, spinning in the intended direction should get you vaguely pointed where you need to go, but it should be much better if its the front wheels taking over when the rear wheels fail.